1. Technical Field:
The present invention relates in general to conductor lead structures in a magnetoresistive sensor, and in particular to a multi-layered conductor lead structure of alternating refractory and conducting layers in a magnetoresistive sensor.
2. Description of the Related Art:
A magnetic transducer, often referred to as a magnetoresistive (MR) sensor head, is utilized as part of a magnetic data storage and recording media. An MR sensor is capable of reading data from a magnetic surface at high linear densities. It detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
In addition to the magnetoresistive material, the MR sensor has conductive lead structures connected to the MR film which sense the resistance variations that occur while reading out data. Typically, a constant current is sent through the MR film and the voltage variations caused by the changing resistance is measured via these leads.
The preferred material for constructing these leads is a highly conductive material such as a metal. In the MR conductor lead application, these materials face much more stringent requirements when compared to other interconnect conductors, such as for semiconductor devices. This is because the conductor lead, as well as the MR thin film, is exposed at the head's air bearing surface (ABS). The lead has little protection from the severe mechanical environment where head-disk contact occurs frequently, and from the severe corrosion environment where chemical attack occurs both during processing and also in actual use where the environment may not be well controlled.
The early MR heads were fabricated using pure gold metallurgy and other highly conductive materials as the lead conductor. However, due to the exposure at the air bearing surface, these soft metals had the potential reliability risk of electromigration, smearing and nodule formation. Tungsten was introduced as a gold substitute due to its mechanical properties of being very hard and its good electrical conductivity which was approximately 15 micro-ohm-cm in thin-film form.
The introduction of tungsten to the MR process solved the mechanical issues associated with the lead metallurgy but posed a more serious corrosion problem at the air bearing surface during the lapping process. The combination of magnesium-iron as an exchange layer (highly corrosive in acid solution) and tungsten as the conductor layer (highly corrosive in basic solutions) would require a neutral lapping solution free from ion contamination. This has been proven to be near impossible to maintain.
Although the current technology has provided satisfactory results, development of MR heads capable of reading magnetic disks of significantly denser data is being pursued. The higher the bit density to be read by the MR head, the thinner the MR thin film must be; for example, future MR heads with nickel-iron (NiFe) thin films will have thin-film thicknesses of 250 .ANG. or less. The processes for making the thin film materials that comprise the active sensing region of the MR head are producing thinner and thinner sensors.
The problem with current lead conductor materials, such as titanium-tungsten/tantalum, when used with these modern thin-film MR heads, is that given their minimum resistivity values of 20 micro-ohm-cm or more, their thickness must be around 2000 .ANG. in order to achieve acceptable sheet resistance values of less then 1.5 ohms/sq. When the relatively thick titanium-tungsten/tantalum leads are used with high bit-density thin films of 250 .ANG. or less, a large surface topography is induced at the edges of the active region of the MR head.
Moreover, when the MR read head is merged with an inductive write head, succeeding layers of the write head are deposited over the MR elements and conductor leads to form the write head. The large surface topography causes a curve in the two inductive poles of the write head, resulting in a higher read error rate for the MR head.
To eliminate the topography, stitched leads processes have been developed and implemented where the lead thickness at the ABS is 1200 .ANG.. However, even further reduction in lead thickness, perhaps down to 700 .ANG., is required for high bit-density MR heads with MR thin film thicknesses of less than 250 .ANG.. Moreover, it is also desirable to eliminate the extra photolithographic and deposition steps required by stitched leads.
Therefore, it would be desirable to provide an MR conductor leads structure which approximates the thickness of the active region of the MR head to minimize surface topography, while maintaining acceptable resistance values. Moreover, it would be desirable for this MR conductive leads structure to have enhanced mechanical strength and stability in order to resist nodule growth and smearing.